Multiunit tube



Oct. 29, 1940- H. E. FRACKER MULTIUNIT TUBE Filed Jan. 21, 1951' 2 Sheets-sheaf. 1

R E 0 N Tm W 5 va 5 N r m 6H w Oct. 29, 1940. H 5 FRACKER 2,219,590

MULTIUNIT TUBE Filed Jan. 21, 1931 2 Sheets-Sheet 2 ll 46-S0-$2 58 2 IN V E NTOR Henry E. Fracker ATTOR N EY Patented Oct. 29, 1940 UNITED STATES PATENT OFFICE 2,210,500 min-norm runs 7 'llenrykrrackenrasadmcalfl. Application January 21, rear, Serial No. my:

's cmma (Olzen-47.5)

to thermionic emission thermionic device purpos s,

This invention relates devices; more particularlyto a that may be utilized for any of several such, for example, as for providing amp detector, or modulator stages.

Although the present form of tube is especially Chief among these factors the attempt has been made to employ standard radio tubes instead of designing special tubes constructed to meet the very unusual combina- 25 tion of requirements imposed by this particular purpose. Thus, the overall thermionic emciencies of the complete amplifier circuits of the prior art have been so low that large size batteries had to be used to obtain a life of only a few hours. The

30 size of the batteries coupled with the space occupied by the tubes has been so large that the devices were in no sense adapted to be conveniently and inconspicuously supported on the person having impaired hearing.

It is a principal an efficient which is of all the elements needed to provide and faithful reproducing system, 40 small size and light weight.

It is another object of this invention to provide a tube which makes possible such a system, by having very low current consumption and thus being capable of operating on very small sized 45 batteries, and without the necessity of frequent renewals.

It is still another object of this invention to provide a multiple section tube wherein a plu- 50 rality of thermionic emission devices are incorporated in a single envelope. It is still another object of this invention to provide a tube wherein thetube elements from highly reflecting poorly radiating surfaces focused 5 on the cathode, so that the latter is maintained relatively ratio of vacuum to and thus enabling fication. tail, illustrating the gener vention; but it is to be un tailed description is sense, since the scope of at a given of heatin battery energy Itisastill type of filament for the cathode, slrable thermionic emission properties maintain a more level in the filament voltages, thus assuring long further obiect under temperature with small expenditure to provide a new which has deand acts uniform current changinfl battery battery and tube life.

It is a still further object of this invention to wherein the elements operate at a provide a tube low small size.

temperature,

permitting a low enclose a metal surface area the use of an envelope of It is a still further object of this invention to provide a rugged tube of the character described,

in which mlcrophonic or mized by appropriate do the tube and of the supports It is still another object provide a multisection tube, impedances between the se within the tube.

This invention possesses many other advanother objects which may be made tages, and has panying and forming part of This form

not to be e invention. form in the drawings accomwill now be al principles of the inderstood that this detaken in a limiting this invention is best tube noises are minisign of the for the cathode.

of this invention to wherein the coupling ctions are enclosed elements of more easily apparent from a consideration of one embodiment of th there is shown For this purpose the present specidescribed in dedeflned by the appended claims.

Referring to Figure 1 is an enlarged away, showing in accordance Fig. 2 is a fragmentary section through the tube il Fig. 3 is a further enlarged fragmentary seethe drawings:

elevation,

with the invention;

enlarged longitudinal lustrated in Fig. 1;

tion showing in detail a preferred type of construction between tube secti Fig. 4 is a sectional view, taken along plane 4-4 of Fig.5isa

Fig. 5G is an enlarged fragmentary sectional view, similar to Fig. 5, and showing a detail of construction; 7

Fig. 6 is a diagram ons.

partly broken away. Fig. 2;

atic view similar to Fig. 4,

but illustrating a modified form of the invention;

Fig. 'l is an utilized in the elevation of one of the elements modification of Fig. 6 for supportpartly broken the exteriorof a tube constructed ing the structure within the exterior envelope or container forming the tube;

Fig. 8 is a fragmentary sectional view illustrating the manner in which the filamentary cathode is damped;

Fig. 9 is a diagram illustrating a modification in which further be utilized;

Fig. 10 is a diagrammatic longitudinal section illustrating the manner in which a single filamentary cathode is supported and clamped; and

Fig. 11 is a diagram of the complete tube illustrating one manner in which the elements of the tube may be connected to form an amplifying system.

A convenient manner in which the enclosing envelope I may be made is in the form of a metal or glass tube. This tube I may be provided with firmly attached to one end of the tube as by telescoping therewith. This base 2 may be provided with a series of terminal posts, such as indicated at 3 in Figs. 1 and 11. These terminals are made very much smaller and shorter than is customary, because of the relatively minute currents required to operate this multiple tube, resulting in important further reductions in size and weight. By the aid of these minal posts 4 may be supported as shown in the drawings or by These terminal posts may be connected by appropriately sealed in leads to certain electrodes to the output side. It is of a hearing aid, that the as possible.

preferable for purposes tube I be made as small, The tube is shown greatly exag- Furthermore the tube at the right hand end of the tube I, to the output stage, is preferably subdivided into two sections 9 and I 0 which may be in push-pull relation. These two output sections 9 and I 0 may advantageously be constructed as a pushpull class B or 0 stage, thereby reducing the drain of current from the source of electrical energy providing the anode currents. The pushpull arrangement will, as is well understood, result in substantial neutralization of the even harmonies which are necessarily present in these classes of amplifiers. Further reduction in distortion caused by the output stage of high plate circuit efiiciency may readily be accomplished by supplemental electrodes may providing a single or preferably multistage repotential differences within the tube. reduction in tube size results in the further adthe cathode may be reduced. Hence, Without sacrificing battery life, the cathode heating batdimensions.

One adverse eflect of reducing the dimensions of a tube of the usual prior art construction is the large end effect emission loss of the filamentary cathode, due to the cooling of considerthe filament adjacent to the terininals and points of contract with tension springs. In short filaments the ratio of useful, or actively emitting, filament length to total filament length becomes very low, and any attempt to improve this ratio by operating the filament at an increased temperature results in a mos life, with heavy replacement All of these heat losses in the usual filament structure necessitate the use of large batteries for a reasonable life. However, by maintaining a single filament at temperature throughout its length except for short distances adjacent to the two ends, a very much higher thermionic efficiency can be realized than in the ordinary prior art cathode structure, in which the temperature changes from ambient to about 900 degrees C.

tary cathode II, which extends axially through all of the tube units 5, 6, I, 8 and 9I0. Further advantages derived from the use of a single filamentary cathode of this sort will be referred to hereinafter.

In order to support the filament II, as well as other electrodes within the tube envelope I, use is made of a framework structure which will now be described.

The framework in general comprises four longitudinally disposed parallel metallic rods I2, I3, I4 and I5 (Figs. 2, 3, 4 and 5). These four rods are held in appropriate relative positions by the aid of metal shielding plates I6, spaced along the length of the tube I and placed between the units 5, 6, I, 8, 9, and between sections 9 and I0. These be provided with four radial ears I1. These ears are formed with appropriate apertures for the pair of metal bushings I8, as shown in Fig. 3, also telescoping respectively over the rods I2, I3, I4 and I5. These metal bushings may be spot welded to the rods,

a the heating current.

as wellas to the plate It. The ears l1 may be folded over, as illustrated in Fig. 3, to contact one of the bushings II where the ear may also be spot welded to that bushing.

. Of course, the operation of assembling this framework with the plates It must occur in suc- 'cession after the tube units, except for the filament H are assembled. The plates l8 are each provided with a sufllciently large central aperture IQ for the insertion of the filament I after all of the units are otherwise assembled. The shielding plates l6 are all maintained at practically ground potential by welding a lead inside the tube to one of the rods l2, |3, |4 or I5, and to the filament terminal 21 shown in Fig. 10, adjacent to the input section.

The framework comprising the rods l2, l3, I4 and I5 as well as IS with their supporting members, is arranged to be frictionally supported with respect to the internal surface of the tube I. In the form shown in Figs. 2, 3, and 4, this frictional support is provided adjacent to each plate I6 by the aid of a pair of supporting insulation plates 20 and 2|. These plates may be conveniently formed of mica. They may be supported on the bushings It! as by having apertures in alignment with these bushings and of such size that-they may be placed upon the reduced portions 22 of these bushings. The ends of the bushings I8 may then at 23, to clamp the plates 20 and 2| onto the bushings. Adjacent to the periphery of each of the plates 20 and 2| are a series of serrations or teeth 24 adapted frictionally to contact the internal surface of the tube The mica plates 20 and 2| have sufficient give or res'lience so that the points of the teeth 24 are urged resiliently against the interior surface of. the tube to maintain the framework structure within the tube against motion.

The diagram, Fig. 10, illustrates the spacing of the intermediate metal shielding plates IS. The thick mica end supporting insulation plates 25 and 26 are also fastened to the rods l2, |3, i4 and I5 by means of metallic bushings similar to l8. Between these terminal insulation plates, the filament may be stretched; for example, the left hand end of filament I! may be welded to a terminal piece 21, in turn riveted or clamped over the central aperture in the terminal insulation plate 25. The right hand end of cathode may be welded to a spring support terminal 28, in turn fastened as by riveting or clamping to the terminal insulation plate 26. The spring support 28 causes a constant tension to be applied to the cathode keeping it sufficiently taut even when the filament is heated by the passage of Appropriate connections may be made to the terminal piece 21 and spring terminal 28 for placing the cathode H in series with a source of electrical energy, such as a small filament heating dry battery.

The combined terminal and tension spring 28 is located adjacent to the output rather than the input stage of the tube. In this way the greater part of the longitudinal movement of the filament, due to thermal expansion prior to reaching normal operating temperature, will occur in the high level stages of the tube rather than in the input or low level stages. By means of this expedient, any noises in the form of slight electrical voltage variations attendant upon expan sion of the filament will be rendered practically inaudible in the output of the tube, since relabe upset as showntively little amplification follows that part of the filament having significant displacement.

In order to damp the filament against microphonic vibrations, vided on each of the shielding plates It. This damping arrangement is disclosed most clearly in Figs. 2 and 4.

Thus, mounted upon one side of plate I! is an insulation segment 23 having low thermal conductivity, preferably formed of very thin mica. This segment is arranged concentrically with the filament H and provides a concave arcuate seat for the filament. 0n the opposite side of -each plate IS, an insulation bar 30, also preferably made of thin mica, is pivoted about a pin 3| fastened to the plate I6. After the filament II is threaded through all of the central apertures in plates I6, 20, 2|, 25 and 26, and is stretched taut between its terminals 21 and 23, and before insertion of the framework in the tube the mica bars 30 can be swung into the damping position in contact with the filament, illustrated in Fig. 4. It may be held in the damping position by the aid of a small metal clip 32, which can be spot welded to the plate l6. It is understood that the filament may move lengthwise through the damping means, to allow for expansion and contraction from temperature changes.

In place of the notched mica discs 20 and 2| for positioning the framework within the tube I, another type of support may be provided as illustrated in Figs. 6 and 7. In thisform of the damping means are pro-- by the aid of a small rivet 35 passing through the center of member 33 and spot welded to the respective supporting bars. It is apparent that prior to insertion of the framework into tube the members 33 are in the flat form shown for example as 34 in the right hand portion of Fig. 6. However, as the framework is inserted into tube I, these members 33 assume an arcuate form in order that their end edges may pass into tube The resilience of these plates maintains the framework frictionally within the tube. In order to facilitate the insertion of the members 33 inside the tube, the leading edge of each of the members 33 may be rounded as shown at 33' in Fig. '7. Thus as the completed framework structure is inserted within the tube these rounded surfaces first contact with the interior surface of the tube, and are then later automatically distorted on further axial movement within tube to conform to the arcuate form shown in Fig. 6.

The various tube elements for each of the units 5, 6, I and 8 and each of the sections 9 and It) .may readily be supported from the mica plates 20, 2| as shown most clearly in Figs. 2, 3 and 4. Thus, the innermost grid electrode 36, which may be in the form of a helix may be telescoped over and welded to a pair of supporting rods 31 and 38. These rods are supported at their ends on bushings 39. This structure is shown most clearly in Fig. 2. These bushings 39 may be spot welda very thin transverse similarly supported in each tube unit' or section. In the form sho in Figs. 2 and 5, there is an .additional supplementary grid 40 supported on the rods 4|.

9, a series of concentric grid electrodes is indicated in which there are several additional supplementary grids such as 42 and I3. specific number of such supplementary grids, used for example as suppressor, screen or space aid of the present invention, scribed possesses an extremely low michophonic response. This is achieved, not only by the un- The filament damping elements are shown in Figs. 8 and 10, and may comprise be arranged as shown at 38 in Fig. 5.

Each of the units 5, 6, I and 8 as well as each of the sections 9 and I0 is further provided with a plate or anode. This plate or anode is conveniently made in the form of a cylindrical metallic element 46, extending the full length of each unit or section between the mica plates 20 and 2|, instead of being somewhat shorter, as shown in Fig. 2 for clarity. It may be attached rigidly to the rods 41 extending between the mica plates 20 and 2| of each unit or section and appropriately supported as heretofore-described in connection with the other rods 31 and 28.

The leads from the base terminals and coupling elements to the tube electrodes may appropriately consist of small but rigid wires 48 and 48' passing intermediate the ears I! and tightly through holes in the mica plates 20 and 2|, as shown in Figs. 4 and 5. In case of the few low level or high impedance leads, shielding may be provided by welding lengths or thin walled metallic tubing to the support rods i2, i3, H and I5, and passing each of these leads through separate lengths of the tubing, as shown at 52 and 63in Fig. 5. The ratio 01' tubing inside diameter to lead diameter case of long sections where the distance between or more tightly fitting insulating members within the tubing to rigidly support and damp the lead against vibration. The special internal coupling condensers, emoying the anode of each unit or section as one plate, are constructed in the following man ner. As illustrated most clearly in Figs. 2 and 5, each cylindrical plate 46 may be overlaid with a very thin tubular dielectric member 49 of mica or similar material possessing a large dielectric constant, low dielectric absorption, and excellent volume resistivity and mechanical properties at high temperatures. Disposed over this layer of dielectric material is another tubular conducting element 56 forming the other plate of the condenser. If the capacity is still insufficient for certain purposes, or additional electrical shielding is desired, a supplemental thin tubular layer of dielectric 5i such as mica, may be disposed over the tubular member 50; and over this dielectric tube 5| may be disposed another tubular metallic member 52. The anode 46 and the external tube 52 may be electrically joined together Furthermore in order to permit expansion of the plates upon emperature rise, as encountered induction furnace during outgassing of tensions, such as 54, 54' their outer longitudinal plates 50 and 52 may cal form by spot welding the outer longitudinal edges of these flanges 54 and 54'. A slight degree of resilience of these tubular elements is provided by this construction, allowing the necessary slight expansion and contraction.

In cases where the tube must be operated under conditions necessitating the maintenance of an extremely high vacuum within the tube throughout its life, it is desirable to form the anode 41 as well as the tubular metallic elements 50 and 52 of a previously de-gassed metal such as tantalum,

volumes of gas at only red heat. Thus, it any slight amount of gas is trapped during the manufacture between the elements forming the coupling condensers, it will readily be absorbed by the adjacent tantalum surfaces when the tube is subjected to the induction furnace during evacuation and de-gassing. Since the gas absorbed at 5 red heat by the tantalum is' not released except at very much higher temperatures, far above the highest possible instantaneous temperatures attained by thetube in operation, a very high degree of vacuum is easily maintained during tube .0 life. The conventional getter may also be utilized in the usual manner, to decrease the necessary pumping time for each tube.

It is desirable to utilize resistance coupling between the amplifier units- These resistances are 15 of comparatively high order, and may conveniently take the form of molded ceramic covered tubular rods or elements having low temperature resistance coefficient and occupying very small space. They may be included inside the tube en- 20 velope I. One of them for the tube unit shown in Figs. 2 and 5 is illustrated at 55. Metal clamps 56 may compass the ceramic resistor 55 and may be joined as by welding to one of the framework rods such as i2.

25 Fig. 11 illustrates how the coupling resistors 55 and the capacities 46-50-42 may be joined in appropriate manner to provide the coupling between the stages. The common filament II is shown as having terminals comprising one of the 30 terminals 3 and one of the terminals 4 at opposite ends of the tube. Some of the resistors 55 are shown connected to a common lead 56 and others to a common lead 51. The last stage includes the push-pull arrangement with a pair of plates 5 58 and 59. The circuit of the push-pull stage may be completed exteriorly to the tube I.

As heretofore stated the cathode II forms a single source of electrons for all of the units and sections. It is usual to provide bias potentials for 40 the control grid electrodes 36 negative with respect to the negative end of that part of the cathode ll passing through the particular section specified. The negative grid bias in the present instance can be readily obtained for all sections 5 (other than the input, which for some purposes does not require a biasing potential) without the need of any extraneous source of electrical energy or potential, provided care is exercised in the manufacture of the tube to keep effective con- 50 tact potentials to very small values.

tive bias potentials are secured by connecting the negative lead of the filament battery, which is also grounded, to the filament terminal adjacent to the input stage, and then connecting all grids 55 to this negative filament terminal through appropriate grid impedances. In this way, the grid bias of the tube sections progressively increases from input to output of the tube in accordance with the demands of the similarly increasing power levels of the amplified voltages; each section being biased more negatively than the foregoing one by an amount equal to the filament potential drop of the preceding section. Each section is specially designed to operate most efiiciently with the particular value of grid bias potential derived for it in this manner.

The problem of providing long life for the batteries for operating the system is ade uately met with the aid of the present construction. Econ- 70 omy, for example, is secured by the fact that the electrodes in the tube structure are very small and closely spaced. Therefore they require somewhat lower potential differences for the same degree of amplification. Furthermore the cathode 7 ll requires very much less electrical energy to obtain the desired thermionic emission. The close spacing of electrodes provides a high amphfier gain, decreasing the number of stages necessary for a specified amplification and thereby reducing cathode and plate battery drains.

A saving in energy for heating the cathode is effected, as previously indicated, by providing a cylindrical anode structure which surrounds the grids and cathode. The inner and outer surfaces of the anode are made reflecting so that heat radiated from the cathode is reflected back and focused on the concentrically located cathode instead of being re-radiated out of the tube. The reflecting outer surface of the anode, being a poor radiator, likewise aids in retaining the cathode energy within the tube. The surfaces of the grid wires may also be arranged to reflect the heat back to the cathode by winding the cylindrical grids with narrow fiat ribbon instead of round wire and providing the ribbon with an effective heat reflecting surface. Both surfaces of the metallic shielding plates between all of the tube units are also provided with reflecting surfaces. Polished copper surfaces may be used for all heat reflecting and radiating surfaces within this tube since the special cathode operates at very low temperatures, therefore radiating most of its energy at wave-lengths where polished copper forms approximately the most efiicient reflector.

In order further to reduce the drain from the filament battery, the filamentary cathode-ll is constructed in a special manner. It is apparent that when a new cathode heating battery is installed, the potential difference developed across its terminals is somewhat larger than after it has been in use for a time. If no regulating resistance is used (as is preferred in order to conserve battery energy and render unnecessary any manual adjustment) then the current drain through the usual Konel, other nickel alloy or platinumiridium filament during this first period of battery life is relatively heavy, with an attendant reduction in useful life of both battery and tube.

By a special construction of the cathode, the use of a regulating resistance is obviated, and yet the current drain is prevented from rising to abnormal values during the first period of operation with a fresh battery.

For this purpose, the cathode ll ispbuilt up of a core made from some material having a very high temperature resistance coefiicient at the temperature of operation. Therefore its resistance increases greatly with rise in filament temperature, and therefore with increase in filament current. Such a core is preferably tungsten for small diameter filaments requiring high -tensile strength at operating temperatures, al-

though iron might be used in certain cases. Thus, any tendency for the current in the filament to increase is largely offset by the increase in resistance of the filament. Likewise, as the heating battery decreases its potential with use, the resistance of the filament also falls, tending to keep the filament current and therefore emission, much more constant. nly is a small amount of aluminum forming an alloy with the copper. The alloy of copper and aluminum thus exposed, after being coated with the appropriate metallic oxides, forms a thermionic emitting surface possessing a very high thermionic eflficiency at unusually low operating temperatures. Since even small decreases in operating temperature effect very large decreases in radiation energy losses, correspondingly large reductions in heating battery consumption are obtained, thus enabling long life to be secured from very small size, light weight batteries.

The mode of assembly of the tube is apparent from the foregoing. The framework including the rods I2, I3, I4 and I5 is first assembled upon one of the end plates 25 or 26, then each previously assembled section or unit is assembled in succession upon these rods. The filamentary cathode II however, is not threaded through the plates I6, 20, 2|, 25 and 26 until all of the tube sections are assembled on the framework rods.

Next the damping elements 30 are placed in operative relation with cathode II. If the interinside their respective inner grids as each section is assembled, prior to the insertion of the cathode I i.

After the cathode H is installed, the completed framework with its units and sections may be inserted inside tube I The leads are then brought out through the tube and the process of outgassing can then be proceeded with. After this, the tube may be sealed oif and the base 2 and terminals 4 installed. Following suitable aging of the filament, the tube is then ready for operation.

What is claimed is:

1. In a thermionic emission device, a sealed container, an elongated cathode in the container, a series of sets of spaced electrodes cooperating trode of the succeeding unit.

2. In a thermionic emission device, a sealed container, a cathode in the container, a plurality of sets of electrodes the vessel.

4. In a thermionic emission device, a sealed container, a cathode 1n the contalner, an anode of a coupling capacity, and an intermediate conductor between the anode and HENRY E. FRACKER. 

